1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 , TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU#/.3425#4)/. G0G0).34!,!4)/.G0G0!.$02/4%#4)/.G0G0/ location and purpose of the termination; number or quantity of terminations required; type of service or transmission link involved; flexibility and protecti
2、on requirements.Basically, all exchange, repeater (amplifier or regenerator), and major cross-connection point terminations areof the “fixed” type utilizing wrapping, soldering of insulation displacement connection (IDC) techniques.Local distribution and customer terminations utilize a mixture of “f
3、ix” and “temporary” (screw terminal) typeterminations depending on individual conditions. Where required, over-voltage protection may be provided as anintegral component of the terminating device or a separate “add-on” facility.Within a cable network, two methods of terminating cables are available.
4、 These may generally be referred to asthe direct and indirect methods.Direct termination implies that the conductors associated with a particular cable connected directly to theterminal forming the “end” of the cable circuit, e.g. the cable conductor and terminal are directly coupled.Indirect termin
5、ation implies that the cable conductor is connected to the end terminal via a device thatincorporates a preformed or manufactured termination.Direct terminations are usually utilized in end terminals such as at the exchange main distribution frame (MDF)and customer premises, although some direct ter
6、minations are used in the customer distribution cable area. In mostother mid-point terminations (distribution cabinets and pillars, repeater housings and termination points for trunkcarrier and coaxial cables), indirect terminations utilizing devices with pre-terminating tail cables are spliced into
7、 thebasic bearer cables.The electric conducting parts of terminating devices will be of metal such as copper, brass or other similaralloys suitably plated to resist corrosion and other environmental effects and provide good electrical connection, eitherby contact, pressure, soldering or wrapping.Var
8、ious insulating materials (plastic extrusions and resin moulding) provide the mechanical mounting andelectrical insulation of the metallic components.2 Termination types2.1 Termination types for symmetric pair conductors2.1.1 Wire-wrapping typeIn this type the conductor is wire-stripped and cut, ins
9、erted in a wire-wrap tool and wire-wrapped around theterminal point.2.1.2 Solder-on-typeIn this type the conductor is wire-stripped and cut, then inserted in the terminal slot and soldered.2.1.3 Wrap-and-solder typeIn this type, after wrapping, the conductor is soldered to the cut end of a terminal.
10、2 Volume IX - Rec. L.92.1.4 Binder-post typeThere are different forms of this type:a) Termination by means of screws. The conductor is wire-stripped, cut and fastened with screws by means ofa screwdriver.b) Termination by means of nuts. The termination consists of a fixed threaded brass post contain
11、ing washersand a threaded hex nut. The conductors are terminated between the washers.2.1.5 Insulation displacement contact (IDC) typeIn this type, generally the conductor is installed and pressed into a U-element contact by means of a specialtool.The U-element contact has different forms and is the
12、most frequently used terminating type.2.1.6 Termination for unused conductorsThis termination is made by means of plastic connectors without U-element contacts and is used for theprotection of unused conductors in a pedestal or splice closure.2.2 Termination types for coaxial conductors2.2.1 Connect
13、ors typesCoaxial pairs are terminated in connectors mounted on a metallic diaphragm for accessing the repeater housingof the terminal equipment.The connector joins the stiff coaxial tube to the flexible one leading into the housing or exchange, and isprovided with a device for pneumatic insulation.2
14、.2.2 Direct-joint typeA joint between the air core tube and the flexible coaxial cable is made at times.3 Termination useThe types of termination mentioned above are used in different devices and locations for terminating cables inall their applications: main distribution frame, regenerating equipme
15、nts, cabinets, terminal boxes and subscriberspremises.These devices present some physical characteristics which may vary greatly from country to country, althoughtheir technical features (i.e. electrical and environmental requirements) are very similar.4 Requirements for MDF terminating devicesThe b
16、asic requirements of the exchange MDF terminating device include the provision for: fixed termination of external cable conductors, in multi-pair units (usually 100), and associated jumpercross-connection leads; ease of termination, and retermination where necessary, of cable and jumper cross-connec
17、tion conductors; overvoltage protection by add-on or plug-in triode gas protectors; circuit isolation by insertion or removal of an appropriate device; independent circuit accessing and testing, on equipment and line sides; circuit paralleling; earthing point or buses; ratio of O/G (outgoing) to I/C
18、 (incoming) circuit terminating capability of at least two; multi-point pair access connection (plugs and leads); colour coding of special circuits; fanning strips and jumper guides; permanent circuit indentification numbering; good visibility.Volume IX - Rec. L.9 34.1 Technical requirementsThe desi
19、gn, construction and materials utilized in the terminating device must provide for an expected servicelife up to 40 years. Devices must be compatible with the existing MDF construction and utilization practices,interchangeable with the existing termination devices, and maintain or increase current c
20、ircuit density per unit area.The line side terminals shall be required to terminate the existing range of copper external cable conductorsextending from 0.32 mm to 0.90 mm diameter, plastic insulated with solid or cellular forms of insulation. The terminalson the equipment side shall be required to
21、terminate the existing range of copper internal cable conductors.Reliable retermination of conductors in the order of 100 to 200 times over the life of the system shall bepossible. Prior termination of larger conductors shall not affect the subsequent termination of a second thinner wire.The line si
22、de terminating device on which line cables terminate should allow for the installation and acceptancetesting of external cables (automatic simultaneous access, via the MDF termination, to all pairs of a 100-pair, or other,terminating unit.).Terminating equipment shall be able to withstand the effect
23、s of normal concentrations of moisture, sodiumchloride, hydrogen sulphide, sulphur dioxide, ammonium chloride and formic acid which may penetrate or originate inbuildings.Terminating equipment shall be expected to operate satisfactorily in temperatures ranging from 10C to 50Cwith daily ambient fluct
24、uations of up to 15C. Upper temperature limits shall be assumed to prevail for 25% of totaltime. Yearly averge relative humidity of 75% is to be assumed with maximum values not exceeding 95%.In addition to the above, terminating equipment will be required to satisfy the following test requirements:
25、cold; dry heat; damp heat; accelerated damp heat; vibration; storage; mould growth; corrosion test; robustness of terminals.4.2 Safety requirementsTerminating systems will need to be designed with safety and security in mind. To this end, designs should: minimize the likelihood of unintended electri
26、cal contact and/or accidental dislocation of wires; use plastic materials with an oxygen index of at least 28, determined in accordance with internationalstandards; use plastic materials which do not emit hazardous fumes or smoke when heated; avoid sharp corners and edges.4.3 Electrical requirements
27、All the terminating blocks should have proper electrical characteristics in order to minimize the risk of personalinjury to staff, customers and public from electrical causes, arising from the installation, operation, and maintenance ofthe devices.If necessary, proper values should be recommended fo
28、r: insulation resistance; voltage-proof test; capacitance between pairs of terminals.4 Volume IX - Rec. L.95 Requirements for cable termination devices5.1 Electrical characteristics of terminationsThe main electrical characteristics for termination devices specified by most Administrations are: diel
29、ectric strength; insulation resistance; reflection index (coaxial only); contact resistance.These characteristics are different for coaxial-pair terminations, long-distance symmetric-pair cables and localsymmetric-pair cables.5.2 Environmental requirements of terminationsThe requirements should be s
30、pecified for at least 20 years of field operation in stationary use at partiallyweather-protected locations. The IEC Standards should be followed in the areas of: temperature cycling, lower and upper limits; change of temperature; damp heat, steady state; standard climatic sequence;1) dry heat,2) damp heat, cyclic,3) cold,4) damp heat, cyclic, gas-tightness; shock or vibration.
